Learning focus
Explain chemical changes using particles, collisions, equilibrium and electron transfer; interpret graphs and industrial conditions; and apply the ideas to unfamiliar reactions.
Hydrated crystals
Hydrated copper(II) sulfate contains water of crystallisation chemically incorporated in its crystals. CuSO4.5H2O is blue. Gentle heating removes water and forms white anhydrous CuSO4.
Evidence on heating
The blue solid becomes white and water vapour may condense on a cooler part of the tube. The water is not simply surface moisture; it is part of the hydrated crystal composition.
Reverse reaction
Adding water to anhydrous copper(II) sulfate changes the solid blue and releases thermal energy. Hydrated material reforms. The visible colour change makes anhydrous copper(II) sulfate useful as a chemical test for water.
Equilibrium language
This classroom process illustrates reversible direction changes, but it is not normally treated as a gas-phase dynamic equilibrium experiment. Use it to explain how conditions can favour hydration or dehydration.
Practical or data skill
Heat a small amount under appropriate teacher supervision, observe condensation and then add water after cooling. Wear eye protection and avoid touching hot glass.
Examination tip
Anhydrous copper(II) sulfate is white; hydrated copper(II) sulfate is blue.
Review questions and suggested answers
Question 1
What happens when CuSO4.5H2O is heated?
Suggested answer
It loses water and forms white anhydrous copper(II) sulfate.
Question 2
What happens when water is added to anhydrous CuSO4?
Suggested answer
It turns blue and releases heat.
Question 3
Why is the process reversible?
Suggested answer
Heating removes water, while adding water reforms the hydrate.
